Biology ETDs

Publication Date

Spring 5-13-2023


As wildfires increase in size and severity, large areas of forest are undergoing substantial increases in shrub cover. In forests where water is the limiting resource, the partitioning of soil water between shrubs and trees may determine how shrubs affect tree growth and water-stress. We analyzed the δ2H and δ18O values of xylem water for two conifer species (Abies concolor and Pinus jeffreyi) and two shrub species (Arctostaphylos patula and Ceanothus cordulatus) to assess how shrub cover affects the water-uptake patterns of conifers in the southern Sierra Nevada. We found that growing environment did not have a significant effect on the water source dynamics of either tree species, with similar source water contributions calculated for conifers growing in both the presence and absence of shrubs. Using a tree-ring analysis of growth and δ13C, we found a positive effect of shrub cover on tree growth and intrinsic water-use efficiency. Overall, our results demonstrate that shrub cover does not alter the water uptake patterns of nearby conifers and instead may have a positive effect on tree growth and water-use efficiency during both wet and dry years.

Project Sponsors

California Department of Forestry and Fire Protection as part of the California Climate Investments Program




Shrub Cover, Competition, Stable Isotopes, Water Source, Intrinsic Water-Use Efficiency, Sierra Nevada

Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Matthew D. Hurteau

Second Committee Member

Seth D. Newsome

Third Committee Member

William T. Pockman

Available for download on Tuesday, May 13, 2025

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